Describing your dataset is the first step of statistical analysis, after data cleaning and wrangling. Thoroughly understanding a dataset is crucial before we can perform any further analysis. The goal of descriptive statistics is to understand the data by summarising its main characteristics. This must be done before any inference can be performed.
The goals of descriptive statistics include:
Describing each variable’s characteristics. This step is part of descriptive statistics, and involves tabulating information and calculating measures of location, such as the mean, and spread, such as the standard deviation.
Detecting patterns in the data. In this step, we look for trends in the data and relationships between variables. This is also part of descriptive statistics.
It is important to note that this step is all about describing data. We are not looking for evidence to support hypotheses, or trying to force any kind of information out of the data. We are simply exploring the data as if it were a landscape.
Rethabile is a dairy farmer who has collected data regarding the milk yield (in liters) of 30 of her cows, shown below. The variables are as follows:
| Cow | Weight | Feed | Active | Breed | Milk |
|---|---|---|---|---|---|
| C01 | 420 | 18.2 | 6.5 | 1 | 19.4 |
| C02 | 590 | 22.8 | 5.2 | 1 | 28.7 |
| C03 | 530 | 20.4 | 6.0 | 1 | 23.1 |
| C04 | 470 | 19.0 | 5.8 | 1 | 20.3 |
| C05 | 610 | 23.2 | 5.1 | 1 | 29.5 |
| C06 | 560 | 21.6 | 5.6 | 1 | 25.4 |
| C07 | 440 | 18.5 | 6.7 | 1 | 19.1 |
| C08 | 580 | 22.3 | 5.5 | 1 | 28.0 |
| C09 | 545 | 21.0 | 5.9 | 1 | 24.6 |
| C10 | 460 | 18.8 | 6.3 | 1 | 20.0 |
| C11 | 600 | 23.0 | 5.3 | 2 | 28.9 |
| C12 | 525 | 20.2 | 6.1 | 2 | 22.7 |
| C13 | 455 | 18.6 | 6.6 | 2 | 19.7 |
| C14 | 585 | 22.7 | 5.4 | 2 | 28.2 |
| C15 | 550 | 21.3 | 5.7 | 2 | 25.0 |
| C16 | 435 | 18.1 | 6.4 | 2 | 18.9 |
| C17 | 600 | 22.9 | 5.2 | 2 | 29.2 |
| C18 | 540 | 20.8 | 5.8 | 2 | 24.2 |
| C19 | 475 | 19.2 | 6.0 | 2 | 20.5 |
| C20 | 615 | 23.4 | 5.0 | 2 | 30.1 |
| C21 | 535 | 20.7 | 5.9 | 2 | 23.9 |
| C22 | 450 | 18.3 | 6.5 | 2 | 19.0 |
| C23 | 595 | 22.5 | 5.3 | 3 | 28.6 |
| C24 | 560 | 21.5 | 5.6 | 3 | 25.1 |
| C25 | 445 | 18.4 | 6.8 | 3 | 18.7 |
| C26 | 610 | 23.3 | 5.2 | 3 | 29.7 |
| C27 | 550 | 21.1 | 5.7 | 3 | 24.8 |
| C28 | 465 | 18.9 | 6.2 | 3 | 20.2 |
| C29 | 605 | 22.9 | 5.4 | 3 | 29.0 |
| C30 | 530 | 20.5 | 6.0 | 3 | 23.5 |